The present invention relates to both a novel method of stabilizing hydralazine hydrochloride in pharmaceutical preparations and pharmaceutical compositions containing stabilized hydralazine compounds having the general formula:
or compounds having the formula:
where R1 and R2 are independently H, branched straight chain alkyl having from 1 to about 7 carbon atoms, substituted or unsubstituted aryl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aralkyl, substituted or unsubstituted alkylcycloalkyl, lower alkenyl or R1 and R2 together form part of a substituted or unsubstituted cycloalkyl having from about 4 to about 7 carbon atoms; where R3 is a branched or straight chain alkyl having from 1 to about 7 carbon atoms, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl, substituted or unsubstituted cycloalkyl, aralkyl, substituted or unsubstituted alkylcycloalkyl or a group having the formula (CH2)nCOOH where n is from 1 to about 7.
Alternatively, the present invention relates to pharmaceutical compositions containing compounds having the general formula:
or compounds having the formula:
where 1 where R1 and R2 are independently H, branched or straight chain alkyl having from 1 to about 7 carbon atoms, substituted or unsubstituted aryl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aralkyl, substituted or unsubstituted alkylcycloalkyl, lower alkenyl or R1 and R2 together form part of a substituted or unsubstituted cycloalkyl having from about 4 of about 7 carbon atoms; where R3 is a branched or straight chain alkyl having from 1 to about 7 carbon atoms, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl, substituted or unsubstituted cycloalkyl, aralkyl, substituted or unsubstituted alkylcycloalkyl or a group having the formula (CH2)nCOOH where n is from 1 to about 7.
Hydralazine hydrochloride is a peripheral vasodilator discovered about 50 years ago that exerts an antihypertensive effect directly on vascular smooth muscle producing relaxation of muscle fibers resulting in a decrease in blood pressure. Hydralazine is extensively metabolized in the body to products that are excreted predominantly in the urine, and undergoes N-acetylation, oxidation, hydroxylation, hydrazone formation and conjugation.
Commercially available in both oral and injectable dosage forms, hydralazine is used to lower blood pressure in hypertensive crisis situations and in patients requiring long-term management of their hypertension after the crisis has abated. Hypertensive crisis is a medical emergency that requires immediate therapy for certain patients in hospital emergency rooms, operating rooms and intensive care units.
Hydralazine is an artery specific direct peripheral vasodilator having an onset of action between 10-30 minutes (10-20 minutes given intravenously), a maximum hypotensive effect in 10-80 minutes and duration of action between 3-4 hours. Hydralazine is one of the few injectable antihypertensive drugs that maintain blood flow to kidneys during hypertensive crisis, and the only one to increase blood flow to an already compromised kidney. Although the drug is approved for administration of 20-40 mg doses, there are several clinical hazards associated with the currently available hydralazine formulation. First, the instability of the 20 mg/ml sterile solutions is a serious problem and has frequently caused removal of the product from the market by the FDA. Submicron particles appear in the hydralazine sterile injection solutions during storage for more than 6-12 months. Secondly, the concentrated 20mg/ml dosage form of hydralazine is difficult to administer accurately to patients at the small doses (3-5 mg) required to avoid “overshoot” hypotension. Consequently, these concentrated solutions are generally diluted prior to use in the hospital. Unfortunately, dilution by hospital personnel in an attempt to reduce the administration problems risks alteration of the hydralazine product, metal contamination and generation of toxic substances. Commercially available hydralazine solutions discolor when inappropriately diluted with metal-containing or carbohydrate-containing diluents generally found in hospitals. The Food and Drug Administration (FDA)s labeling for the currently available hydralazine formulation indicates that hydralazine should not be added to infusion solutions, and that hydralazine hydrochloride injections may discolor upon contact with metal. The FDA further warns in the product labeling that discolored solutions should be discarded.
Hypertensive crisis is a life-threatening situation and includes hypertensive emergencies and hypertensive urgencies characterized by acute elevations in blood pressure, which must be brought under control within hours. Over 60 million people in the United States suffer from essential hypertension. About 1% of these people suffers from hypertensive crisis and requires hospital-based acute care. Of the hypertensive crisis patients, 76% are “urgencies” and 24% “emergencies” with end-organ damage. Hypertensive urgencies are those situations in which it is desirable to reduce blood pressure quickly; however, hypertensive urgencies can be managed without requiring rapid, controlled reduction of blood pressure. Elevated blood pressure alone, in the absence of symptoms or progressive target organ damage rarely requires emergency treatment. Hypertensive urgencies are treated with oral antihypertensives such as nifedipine or clonidine, or with intravenous labetolol.
Hypertensive emergencies are characterized by acute elevations in blood pressure (diastolic >110 to 120 mm Hg) which can potentially be life threatening and thus require rapid, controlled reduction of blood pressure. Prompt pharmacologic therapy is indicated for those patients having Stage 2 (≧160/100 mm Hg) or Stage 3 (≧180/110 mm Hg) hypertension who have clinically manifested cardiovascular disease or target organ damage. The most commonly used antihypertensive agent is nitroprusside. Although hydralazine is already labeled for severe essential hypertension when oral hydralazine cannot be given or when the need to lower blood pressure is urgent as in hypertensive crisis, it is not currently labeled for hypertensive emergencies when a patient presents with emergent end-organ damage. As a patient's blood pressure is acutely elevated, the patient experiences a dramatic decrease in blood flow to vital tissues such as the kidney and brain. The reduction in elevated blood pressure in these patients through antihypertensive therapy is important because it minimizes ischemic damage resulting from reduced blood flow to these tissues. Examples of emergent end-organ damage include hypertensive encephalopathy, cerebral infarction, intracranial hemorrhage, myocardial ischemia, acute pulmonary edema, hypertensive nephropathy, hypertensive retinopathy and eclampsia. The goal of therapy in hypertensive emergencies is to reduce the mean arterial pressure by no more than 25 percent with two hours, then toward 160/110 mm Hg within 2 to 6 hours avoiding excessive drops in pressure that may precipitate or aggravate renal, cerebral or coronary ischemia. Ultimately, the goal of therapy is to reduce the blood pressure to below 140/90 mm Hg.
Hydralazine hydrochloride is very unstable in all of the injectable pharmaceutical formulations currently commercially available. Continuing instability problems with injectable hydralazine hydrochloride, for example, have plagued pharmaceutical manufacturers for many years, forcing these companies to remove their injectable hydralazine products from the marketplace. Although a shelf life of 12 months is currently required for FDA approval for injectable hydralazine hydrochloride, only a few companies have been able to satisfy this requirement with adequate stability data. One such company, SoloPak Pharmaceuticals, Inc. was able to meet the 12-month stability requirements for FDA approval; however, the company was not able to provide a drug product that was consistently stable for more than 6 months.
In its injectable formulation, hydralazine forms small yellow-green particles following storage from 1 to about 2 months when hydralazine is stored at 40° C. and after from 6 to about 9 months storage at 25° C. Although the identification of the yellow-green particles has yet to be confirmed, it is believed that the particles are insoluble polymeric products formed during storage of hydralazine. It is believed that hydralazine hydrochloride undergoes degradation in stored sterile injectable solutions to insoluble polymeric products due to the highly reactive hydrazino group. Hydralazine hydrochloride also undergoes several pharmaceutically undesirable reactions such as chelation with metal ions, oxidation, and pH-dependent decomposition. It is believed that these reactions, which often cause discoloration of hydralazine compositions, are also due to the highly reactive hydrazino group.
Kanazawa et al. [Chemical and Pharmaceutical Bulletin 34(4):1840-1842 (1996)] report that during the storage of a prescription admixture of pulverized hydralazine hydrochloride with cimetidine, a histamine H2-receptor antagonist for duodenal ulcer, the initially uncolored admixture gradually turns to pale yellow. Kanazawa et al. further report that hydralazine hydrochloride undergoes degradation and discoloration with cimetidine in aqueous solution to give 1,1-di(phthalazin-3-yl)amine, 1,1-di(phthalazin-3-yl)hydrazine, 1-amino-1,2, 2-tri-(phthalazin-3-yl)hydrazine, and 1,1,2-tri(phthalazin-3-yl)hydrazine.
Alexander et al. [American Journal of Hospital Pharmacy 50: 683-686(1993)] report that the degradation of hydralazine hydrochloride in a sugar-containing oral syrup was quite fast and was apparently a first order process. The authors report that sugar (e.g., dextrose and fructose) reduces the stability of hydralazine hydrochloride considerably. Their syrup containing maltitol normally increases the stability of drugs sensitive to the presence of sugars; however, the hydralazine formulation remained unstable at room temperature.
Lessen et al. [Journal of Pharmaceutical sciences 85(3): 326-329(1996)] report that the strength of hydralazine hydrochloride in 10 mg tablets containing starch as an excipient decreases significantly with time and produced fluorescence at 414 nm. Lessen at al. report that, in addition to the usual hydralazine degradants such as phthalazone and phthalazine, these tablet compositions produced triazolophthalazine derivatives.
Hydralazine is known to chelate metal ions. Sinha and Motten [Biochemical and Biophysical Research Communications 105(3): 1044-1051(1982)] report that hydralazine oxidizes rapidly in the presence of oxygen and metal compounds such as Cu+2, Fe+2, and Fe+3 through free radical intermediates much like other hydrazine derivatives.
Because of its reactivity toward metals, standard manufacturing requirement for the preparation of bulk hydralazine solution or sterile fill solution is that neither should come into contact with any metal surface including tanks, transfer lines or filling lines. Unfortunately, these precautions can be consistently enforced by the manufacturer only during preparation and storage of the hydralazine solutions. After storage of the hydralazine solutions, the handling of the hydralazine solutions is no longer under their control.
Despite its unique pharmacologic properties as a hypertensive drug, the therapeutic use of hydralazine hydrochloride has been limited by its instability during storage and difficulties in handling by medical personnel. A stable hydralazine pharmaceutical composition that is more easily manufactured and does not degrade or produce particulate matter during extended storage does not currently exist. Moreover, an injectable hydralazine pharmaceutical formulation that is not adversely affected by conventional dilution techniques in the hospital does not currently exist. This, despite the fact that hydralazine was discovered as an antihypertensive agent over 50 years ago. A stable hydralazine composition that could be manufactured more easily and stored for periods of time greater than the current 12 month limit represents a significant advance.